WASHINGTON - The most costly failure of the Patriot missile, a high-tech star of the Persian Gulf War, might have been averted if its operators had used a low-tech tactic: a periodic rest for the missile system's computer, Army documents show.

The Army credits Patriot with shooting down nearly every Scud missile fired by Iraq. But Patriot's biggest failure came on Feb. 25 when it allowed a Scud to fly unchallenged into Saudi Arabia and slam into a U.S. Army barracks.

The attack killed 28 GIs and wounded 98. It was the most devastating single Iraqi attack during the war, in which 148 Americans were killed in action and 467 were wounded.

Army investigators concluded that the exact reason for Patriot's failure to shoot at the Scud will never be known for sure. But they said the most likely explanation was a previously unknown glitch in Patriot computer software.

Army technicians had determined as much as two weeks prior to the attack that the Patriot computer was vulnerable to losing track of incoming Scuds when the computer was kept running for long periods, according to internal Army reports released in response to a Freedom of Information Act request by The Associated Press.

Tragically, no alert bulletins were sent to Patriot operators in the field because the technicians viewed this as a minor problem of less importance than other Patriot improvements they were working on. The technicians did not think Patriot computers would be kept running for more than several hours at a time.

As it happened, the Patriot battery into whose coverage area the Scud fell - Alpha Battery of the 11th Air Defense Artillery Brigade - had been running its computer for 100 consecutive hours at the time of the attack, according to an internal Army memo dated June 14.

Usually the Patriot computers were shut off briefly after several hours of operation, but it was not understood then that long, unbroken periods of operation could hurt the computer's ability to make high-speed calculations.

"Had rebooting, or shutting off the system, occurred, it would have decreased the chance that the inexact (computer) calculation would have occurred," said Lt. Gen. Ellis D. Parker, Army Staff director, in a June 14 memo.

A previously classified internal Army memo dated Feb. 20 described a series of software improvements to the Patriot computer, including a change that was designed to avert the tracking problem.

But in follow-up memos, no mention was made of the tracking problem or of a need for periodic computer shutdowns. "No significance was given this change because no prior related tracking problems had been seen," said an Army Patriot program office report.

The Army's only public statement about the results of its investigation, on June 5, made no mention of the possibility that the simple act of shutting down the computer briefly might have precluded the software failure that allowed the Scud to pass.

The technicians did devise a new software tape designed to avert the tracking problem under conditions of long continuous operation of the computer. It arrived in Saudi Arabia on Feb. 24 but was not installed in Alpha Battery's computer until after the attack, according to the Army documents.

The Army announced the results of its investigation in mid-June, but a fuller picture of the events emerges in the newly released documents.

The papers, including statements given by members of Alpha Battery and others involved in the incident, provide a look at a technological failure that tarnished the record of the world's only operational anti-ballistic-missile system.

The documents include a statement by Maj. Larry Hollars, who watched from a secret television monitor in his underground command bunker in Saudi Arabia as the Scud bore down on the area being defended by Alpha Battery.

Hollars, commanding officer of the Patriot missile battalion whose crews included Alpha Battery, grew worried as he saw the Scud draw within about 20 miles of Dhahran air base, the biggest U.S. Air Force staging area in the gulf region. He could see that Alpha's radar was not tracking the high-speed missile.

Within minutes he received a phone call from an Air Force fighter wing saying the Scud landed about two miles from the air base and that there had been casualties.